Conventionally, a lower rail of a seat sliding apparatus applied to a rear seat of a vehicle including three-row seats is configured in a manner that a front portion is lower than a rear portion. On the other hand, a lower rail of a front seat including a driver's seat is configured in a manner that a rear portion is lower than a front portion. At a seat which includes such an inclined lower rail, a load for operating the seat forward which is required in a case where a seat position is adjusted forward and a load for operating the seat rearward which is required in a case where the seat position is adjusted rearward are different from each other.
A seat sliding apparatus for a vehicle of Patent document 1 includes a sliding resistance adjustment mechanism. The sliding resistance adjustment mechanism includes plural protrusions provided at a lower rail, and a ball attached to an upper rail via a spring that elastically compresses. The protrusion includes an inclined surface and a resistance surface. The inclined surface is provided at a rear side of the protrusion in an upward direction of the seat, and the resistance surface is provided at a front side of the protrusion in the upward direction of the seat. The resistance surface includes a steeper inclination than the inclined surface. When a sliding operation is performed, the ball rides over the protrusion. When the ball rides over the protrusion, an angle of a surface with which the ball is in contact, that is, a resistance that the ball receives from the surface, differs depending on a direction in which the seat is slide-operated. By using the relationship, a load required in the sliding operation in the upward direction of the seat and a load required in the sliding operation in the downward direction of the seat can be set to be equal to each other.